This invention relates to apparatus for testing or measuring the slip resistance (static coefficient of friction) of surfaces such as floors, bathtubs and the like.
For example, industry standards are established for minimum friction coefficients that are acceptable in commercial flooring or bathtub interiors. In order to test such surfaces, these standards may be related, in the former case to the coefficient of friction as between the flooring surface and a material representative of a shoe sole, and the in the latter case to the coefficient of friction as between the bathtub surface and a material representative of human skin simulating the sole of the foot. Further, it is desirable for testing purposes, to have apparatus available which can be readily transported from site to site in order to test floor, bathtub and like surfaces for slip resistance, rather than having to submit a surface sample to a laboratory for testing.
Over the years, numerous different machines have been proposed for testing surface friction or slip resistance. The more successful of these, however, have often tended to be cumbersome making them unsuitable for in situ use. Applicant's prior U.S. Pat. No. 3,975,940, however, discloses a portable-type tester suitable for measuring the slip resistance of a surface on site, and which has been successfully used on a commercial basis for a number of years. Broadly stated, this apparatus consists of a box-like framework which is placed on a surface to be tested. The framework includes upper horizontal support rods on which a carriage element is mounted for horizontal sliding movement. The carriage supports a weighted vertical link which can slide up and down in the carriage. Another link is pivoted to the bottom of the weighted link and has a foot element at its lower end with a pad of friction material (e.g. shoe sole-simulating or human skin-simulating material) which rests on the surface being tested. When both links are in vertical alignment the force of the weight acts directly downwardly on the pad so that no slipping of the pad along the test surface can occur. However, the apparatus is further provided with springs which urge the carriage along the horizontal rods. This action continuously increases the angle between the links (since the pad is held by friction on the test surface) and gradually imposes a more and more angled force on the pad. Eventually, the force on the pad will be directed at a sufficiently shallow angle to cause the pad to slip on the test surface, the particular angle at which such slip takes place being representative of the friction coefficient of the test surface, and the machine includes a mechanism for registering the angle of slip.
Machines in accordance with the aforesaid patent, operate over a time frame for each test, constituted by the time taken for the carriage to move along the horizontal rods to the position at which the slip angle between the respective links is established. This mode of operation has been found to be generally satisfactory for most purposes, and the machine has been well accepted commercially. However, there is one situation in which it is felt that inconsistent results may be obtained, this being in the case of wet test surfaces. The inconsistencies in such situations may be attributable to the fact that in the time taken for the carriage to move along the horizontal rods from the vertical orientation of the links to the slip angle orientation, liquid may be forced out from between the pad and the test surface, so that a progressively drier or tackier interface results, giving a test reading which is not truly representative of the wet surface.